I have a 1978 Pearson 28 with an Atomic 4 gas engine. How difficult is it to convert that to a Yanmar 10 hp diesel? Any suggestions?
Conversion from Atomic 4 to Yanmar Diesel
- Thread starter MikeMowles
- Start date
Why are you suggesting the Yanmar? Is that what you have available (what model)? How do the dimensions of the mounts compare?
I kinda wondered about that, too.
I repowered our boat with a Betamarine. Second choice was a Yanmar, FWIW. (Not a terrible second choice, but not first either.)
Well, also the reason I asked is because the 10 hp reference seems to indicate that he is putting in a re-built 1GM10 model. When I repowered, Mack Boring didn't offer a new 10 hp Yanmar model (and still doesn't as far as I know).
We don't even know if he is intending to buy a new model. For all we know he may have already acquired the engine he wants to put in.
We don't even know if he is intending to buy a new model. For all we know he may have already acquired the engine he wants to put in.
Not really. I had a 30' Sabre with 13 hp. It doesn't take much power to push a sailboat as the hulls are pretty efficient.
Hi all, I am considering repowering with the 10 hp Yanmar because I have a working Yanmar in another boat that I am going to scrap. My two biggest concerns are making the transmission connection and changing from a gasoline tank to a diesel tank.
Regarding it only being a 10 hp, I just need enough power to get on and off the mooring.
The A4 has a straight line transmission from the crankshaft horizontally down to the propeller. The Yanmar takes a 90 degree turn and goes to a prop below the hull. I haven’t gotten in close enough to see how that universal joint is set up yet. It depends on if the A4 transmission will couple to the back of the Yanmar. If anyone has experience with this please let me know.
So the Yanmar has a sail drive? If you know the model number of the Yanmar, you can look up the service manual, there is probably a copy here on SBO under the resources section. It may be filed under a boat manufacturer.
The bolt patterns should be an SAE pattern that should be available in the manual for the A4 and the Yanmar. The other consideration is the spline gear on the A4 transmission and whether it fits the Yanmar. More important than the fit is the gear ratio and the prop size and pitch. You will also need to change the flange on the shaft. There may be adapter plates available to help mate the transmission to the Yanmar. Finally, the prop shaft may end up being the wrong length.
If you have the 1GM10 that @Scott T-Bird suggests, then a new Kanzaki KM2P-1 transmission will run about $3200.
The fuel tank should be the easiest part, remove it, clean it, put it back if it is in good condition and replace the hoses.
The bolt patterns should be an SAE pattern that should be available in the manual for the A4 and the Yanmar. The other consideration is the spline gear on the A4 transmission and whether it fits the Yanmar. More important than the fit is the gear ratio and the prop size and pitch. You will also need to change the flange on the shaft. There may be adapter plates available to help mate the transmission to the Yanmar. Finally, the prop shaft may end up being the wrong length.
If you have the 1GM10 that @Scott T-Bird suggests, then a new Kanzaki KM2P-1 transmission will run about $3200.
The fuel tank should be the easiest part, remove it, clean it, put it back if it is in good condition and replace the hoses.
At least it is probably worthwhile to take a closer look at the A4. If it can be rebuilt, then you will be way ahead of the game in money and effort.
If the Yanmar is in good shape, it may be worth salvaging and selling. The aluminum and the lead in the old boat might be worth a trip to the scrap metal dealer.
jssailem
SBO Weather and Forecasting Forum Jim & John
- Oct 22, 2014
- 21,196
I would contact Yanmar and ask the questions.
The simplest approach is inline.
My boat came with a V drive. The engine front sits facing the boats stern. You just need to look at the boats mount area and figure out what will work. I learned during my repower that with time and ingenuity plus the money just about anything is possible.
The simplest approach is inline.
My boat came with a V drive. The engine front sits facing the boats stern. You just need to look at the boats mount area and figure out what will work. I learned during my repower that with time and ingenuity plus the money just about anything is possible.
A good machine shop can make an adapter plate that would allow the A4 transmission to bolt up to the Yanmar, I think.... but.. the A4 transmission is a 1:1 ratio.. (some are 2:1, but they are a little rare..)which spins the prop at a much higher speed and makes the prop inefficient for pushing a big displacement hull.. If the A4 gearbox is one of the 2:1 ratio boxes, the adapter plate might be a pretty cost effective way to go..
While the comparative HP ratings are measured and believable, I have always found that the torque from a smaller diesel seems to push shorter displacement hulls as good as the old A4 gas engines. Of course that might also be because the comparison is usually with a worn out A4.... ! 
That Yanmar, if in good condition, should do the job just fine.
Somewhere, from some mechanic, I recall the casual comparison, by HP, of the A4 vs a diesel, of "race horses vs clydesdales."
Not an 'urban myth' though is one main reason that boat builders put the A4 into boats from 27 to 35 feet, back in the 70's. The smaller boats had no need for the 30 HP in the A4, but that's the way it came. Also, the flathead design fit a lot better in the boats, having a very low height measurement. When Yanmar introduced their horizontal cylinder YSM8 and 12, boat builders and their gas-skeptical customers really liked it, even tho the published HP ratings were less than the previous A4. That Yanmar was a great fit, being low. Reliable reputation, too.
This is all just old and maybe misremembered trivia, but my point would be to go ahead and embrace the upgrade to the Yanmar diesel.
That Yanmar, if in good condition, should do the job just fine.
Somewhere, from some mechanic, I recall the casual comparison, by HP, of the A4 vs a diesel, of "race horses vs clydesdales."
Not an 'urban myth' though is one main reason that boat builders put the A4 into boats from 27 to 35 feet, back in the 70's. The smaller boats had no need for the 30 HP in the A4, but that's the way it came. Also, the flathead design fit a lot better in the boats, having a very low height measurement. When Yanmar introduced their horizontal cylinder YSM8 and 12, boat builders and their gas-skeptical customers really liked it, even tho the published HP ratings were less than the previous A4. That Yanmar was a great fit, being low. Reliable reputation, too.
This is all just old and maybe misremembered trivia, but my point would be to go ahead and embrace the upgrade to the Yanmar diesel.